Screw Compressor for a Utility Vehicle

ABSTRACT

A screw compressor for a utility vehicle has at least one housing and a relief valve. The relief valve includes a spring-loaded closure mechanism with at least one spring and at least one closure element. The spring has a spring force which is dimensioned such that it actuates the closure element when a predefined minimum pressure above the atmospheric pressure is reached.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a screw compressor for a utility vehicle, having at least one housing and one relief valve.

Screw compressors for utility vehicles are already known from the prior art. Such screw compressors are used to provide the compressed air required for the brake system of the utility vehicle, for example.

In this context, in particular oil-filled compressors, in particular also screw compressors, are known, in the case of which it is necessary to regulate the oil temperature. This is generally realized by virtue of an external oil cooler being provided which is connected to the oil-filled compressor and to the oil circuit via a thermostat valve. Here, the oil cooler is a heat exchanger which has two mutually separate circuits, wherein the first circuit is provided for the hot liquid, that is to say the compressor oil, and the second circuit is provided for the cooling liquid. As cooling liquid, use may for example be made of air, water mixtures with an antifreeze, or another oil.

This oil cooler must then be connected to the compressor oil circuit by means of pipes or hoses, and the oil circuit must be safeguarded against leakage.

This external volume must furthermore be filled with oil, such that the total quantity of oil is also increased. The system inertia is thus increased. Furthermore, the oil cooler must be mechanically accommodated and fastened, either by means of brackets situated in the surroundings or by means of a separate bracket, which necessitates additional fastening means and also structural space.

U.S. Pat. No. 4,780,061 has already disclosed a screw compressor with an integrated oil cooling arrangement.

Furthermore, DE 37 17 493 A1 discloses a screw compressor installation which is arranged in a compact housing and which has an oil cooler on the electric motor of the screw compressor.

A generic screw compressor is already known for example from DE 10 2004 060 417 B4.

It is therefore the object of the present invention to advantageously further develop a screw compressor for a utility vehicle of the type mentioned in the introduction, in particular such that said screw compressor permits an improved pressure dissipation in the interior of the screw compressor.

This object is achieved according to the invention by a screw compressor for a utility vehicle equipped with at least one housing and one relief valve, wherein the relief valve has a spring-loaded closing mechanism with at least one spring and with at least one closure element. The spring has a spring force configured such that said spring actuates the closure element when a predefined minimum pressure above atmospheric pressure is reached.

The invention is based on the underlying concept of the pressure dissipation process of the screw compressor being stopped before the internal pressure of the screw compressor has fallen to a pressure equal to or close to atmospheric pressure. It is hereby made possible for no bubble formation or oil foaming to occur in the interior of the housing of the screw compressor or in the oil sump of the screw compressor. Through the provision of a spring-loaded closing mechanism in conjunction with the relief valve, it is made possible, relatively easily by means of a spring and at least one closure element, to find a setting means which makes it possible for the closing mechanism to close before atmospheric pressure is reached. In this way, it is possible to reliably prevent foaming from occurring in the oil in the interior of the housing.

Furthermore, provision may be made for the spring to be a helical spring. This permits simple and inexpensive production. Furthermore, the handling of a helical spring of said type is relatively straightforward. The configuration of such a standard component is also relatively easily possible.

The closure element may be a ball. In this way, simple and reliable closure of the closing mechanism can be achieved. Furthermore, balls are relatively easily available and can also likewise be easily installed. Spring-loading by means of a spring is likewise easy to realize in the case of a ball. Corresponding surface adaptations are not necessary, because the dimensions of spring and ball can be selected such that these engage into one another and secure one another.

The spring-loaded closing mechanism may be arranged in the vicinity of the inlet connector of the screw compressor. Here, a simple integration into the screw compressor, and also at the same time an expedient ventilation facility by means of the air inlet, can be realized.

Furthermore, provision may be made whereby the spring-loaded closing mechanism is arranged in the ventilation line from the relief valve to the inlet connector of the screw compressor. Simple and reliable installation in, for example, the housing of the screw compressor is possible in this region. Furthermore, reliable access to the atmosphere is ensured via the air inlet of the screw compressor.

Further details and advantages of the invention will now be discussed in more detail on the basis of an exemplary embodiment illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic sectional drawing through a screw compressor according to the invention; and

FIG. 2 shows a schematic sectional drawing of the spring-loaded closing mechanism of the relief valve for the screw compressor as per FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in a schematic sectional illustration, a screw compressor 10 in the context of an exemplary embodiment of the present invention.

The screw compressor 10 has a fastening flange 12 for the mechanical fastening of the screw compressor 10 to an electric motor (not shown in any more detail here).

What is shown, however, is the input shaft 14, by which the torque from the electric motor is transmitted to one of the two screws 16 and 18, specifically the screw 16.

The screw 18 meshes with the screw 16 and is driven by means of the latter.

The screw compressor 10 has a housing 20 in which the main components of the screw compressor 10 are accommodated.

The housing 20 is filled with oil 22.

At the air inlet side, an inlet connector 24 is provided on the housing 20 of the screw compressor 10. The inlet connector 24 is in this case designed such that an air filter 26 is arranged at said inlet connector. Furthermore, an air inlet 28 is provided radially on the air inlet connector 24.

In the region between the inlet connector 24 and the point at which the inlet connector 24 joins to the housing 20, there is provided a spring-loaded valve insert 30, which is designed here as an axial seal.

This valve insert 30 serves as a check valve.

Downstream of the valve insert 30, there is provided an air feed channel 32 which feeds the air to the two screws 16, 18.

At the outlet side of the two screws 16, 18, there is provided an air outlet pipe 34 with a riser line 36.

In the region of the end of the riser line 36, there is provided a temperature sensor 38 by means of which the oil temperature can be monitored.

Also provided in the air outlet region is a holder 40 for an air deoiling element 42.

In the assembled state, the holder 40 for the air deoiling element has the air deoiling element 42 in the region facing toward the base (as also shown in FIG. 1).

Also provided, in the interior of the air deoiling element 42, is a corresponding filter screen or known filter and oil separating devices 44, which will not be specified in any more detail.

In the central upper region in relation to the assembled and operationally ready state (that is to say as shown in FIG. 1), the holder for the air deoiling element 42 has an air outlet opening 46 which leads to a check valve 48 and a minimum pressure valve 50. The check valve 48 and the minimum pressure valve 50 may also be formed in one common combined valve.

The air outlet 51 is provided downstream of the check valve 48.

The air outlet 51 is generally connected to correspondingly known compressed-air consumers.

In order for the oil 22 that is situated and separated off in the air deoiling element 42 to be returned again into the housing 20, a riser line 52 is provided which has a filter and check valve 54 at the outlet of the holder 40 for the air deoiling element 42 at the transition into the housing 20.

A nozzle 56 is provided, downstream of the filter and check valve 54, in a housing bore. The oil return line 58 leads back into approximately the central region of the screw 16 or of the screw 18 in order to feed oil 22 thereto again.

An oil drain screw 59 is provided in the base region, in the assembled state, of the housing 20. By means of the oil drain screw 59, a corresponding oil outflow opening can be opened, via which the oil 22 can be drained.

Also provided in the lower region of the housing 20 is the attachment piece 60 to which the oil filter 62 is fastened. Via an oil filter inlet channel 64, which is arranged in the housing 20, the oil 22 is conducted firstly to a thermostat valve 66.

Instead of the thermostat valve 66, it is possible for an open-loop and/or closed-loop control device to be provided by means of which the oil temperature of the oil 22 situated in the housing 20 can be monitored and set to a setpoint value.

Downstream of the thermostat valve 66, there is then the oil inlet of the oil filter 62, which, via a central return line 68, conducts the oil 22 back to the screw 18 or to the screw 16 again, and also to the oil-lubricated bearing 70 of the shaft 14. Also provided in the region of the bearing 70 is a nozzle 72, which is provided in the housing 20 in conjunction with the return line 68.

The cooler 74 is connected to the attachment piece 60, as will be discussed in more detail below in FIGS. 2 to 4.

In the upper region of the housing 20 (in relation to the assembled state), there is situated a safety valve 76, by means of which an excessively high pressure in the housing 20 can be dissipated.

Upstream of the minimum pressure valve 50, there is situated a bypass line 78, which leads to a relief valve 80. Via said relief valve 80, which is activated by means of a connection to the air feed 32, air can be returned into the region of the air inlet 28. In this region, there may be provided a ventilation valve (not shown in any more detail) and also a nozzle (diameter constriction of the feeding line).

Furthermore, approximately at the level of the line 34, an oil level sensor 82 may be provided in the outer wall of the housing 20. Said oil level sensor 82 may for example be an optical sensor, and may be designed and configured such that, on the basis of the sensor signal, it can be identified whether the oil level during operation is above the oil level sensor 82 or whether the oil level sensor 82 is exposed, and thus the oil level has correspondingly fallen.

In conjunction with this monitoring, it is also possible for an alarm unit to be provided which outputs or transmits a corresponding error message or warning message to the user of the system.

The function of the screw compressor 10 shown in FIG. 1 is as follows.

Air is fed via the air inlet 28 and passes via the check valve 30 to the screws 16, 18, where the air is compressed. The compressed air-oil mixture, which, having been compressed by a factor of between 5 and 16 downstream of the screws 16 and 18, rises through the outlet line 34 via the riser pipe 36, is blown directly onto the temperature sensor 38.

The air, which still partially carries oil particles, is then conducted via the holder 40 into the air deoiling element 42 and, if the corresponding minimum pressure is attained, passes into the air outlet line 51.

The oil 22 situated in the housing 20 is kept at operating temperature via the oil filter 62 and possibly via the heat exchanger 74.

If no cooling is necessary, the heat exchanger 74 is not used and is also not activated.

The corresponding activation is performed by means of the thermostat valve 66. After purification in the oil filter 62, oil is fed via the line 68 to the screw 18 or to the screw 16, and also to the bearing 70. The screw 16 or the screw 18 is supplied with oil 22 via the return line 52, 58, and the purification of the oil 22 takes place here in the air deoiling element 42.

By means of the electric motor (not shown in any more detail), which transmits its torque via the shaft 14 to the screw 16, which in turn meshes with the screw 18, the screws 16 and 18 of the screw compressor 10 are driven.

By means of the relief valve 80 (not shown in any more detail), it is ensured that the high pressure that prevails for example at the outlet side of the screws 16, 18 in the operational state cannot be enclosed in the region of the feed line 32, and that, instead, in particular during the start-up of the compressor, there is always a low inlet pressure, in particular atmospheric pressure, prevailing in the region of the feed line 32. Otherwise, upon a start-up of the compressor, a very high pressure would initially be generated at the outlet side of the screws 16 and 18, which would overload the drive motor.

FIG. 2 shows a schematic sectional drawing through a spring-loaded closing mechanism 100 for the relief valve 80 of the screw compressor 10 as per FIG. 1.

The spring-loaded closing mechanism 100 has in this case a spring 102 and a closure element 104.

The spring 102 is formed as a helical spring.

The closure element 104 is formed as a ball.

The spring-loaded closing mechanism 100 is arranged in the region of the air feed of the screw compressor 10, specifically in this case in the ventilation line from the relief valve 80 to the inlet connector 24.

Here, the spring 102 is designed so as to exhibit a spring force configured such that said spring actuates the closure element 104 when a predefined minimum pressure above atmospheric pressure is reached.

Here, the function of the spring-loaded closing mechanism 100 can be described as follows.

Upon a stoppage of the compressor 10, it is necessary for the interior of the housing 20 of the screw compressor 10 to be ventilated, and for pressure to be dissipated.

This is realized by means of the ventilation valve.

This dissipation of pressure should however be stopped before atmospheric pressure is reached. This serves for preventing foaming in the oil 22.

By means of the spring-loaded closing mechanism 100, it is achieved that the internal pressure remains above the atmospheric pressure.

Here, it is for example possible for values between 1.5 and 2.5 bar to be selected. It is conceivable in particular to select a pressure of approximately 1.5 bar.

The setting of this limit pressure is realized through the setting and selection of the spring 102 and of its spring force.

Here, the spring force is configured such that the ball 104 actuates the closing mechanism, and thus prevents a further dissipation of pressure, when the internal pressure in the housing 20 of the screw compressor 10 is no longer sufficient to push the closure element 104 open counter to the force of the spring 102.

LIST OF REFERENCE DESIGNATIONS

-   10 Screw compressor -   12 Fastening flange -   14 Input shaft -   16 Screws -   18 Screws -   20 Housing -   22 Oil -   24 Inlet connector -   26 Air filter -   28 Air inlet -   30 Valve insert -   32 Air feed channel -   34 Air outlet pipe -   36 Riser line -   38 Temperature sensor -   40 Holder for an air deoiling element -   42 Air deoiling element -   44 Filter screen or known filter or oil separation devices -   46 Air outlet opening -   48 Check valve -   50 Minimum pressure valve -   51 Air outlet -   52 Riser line -   54 Filter and check valve -   56 Nozzle -   58 Oil return line -   59 Oil drain screw -   60 Attachment piece -   62 Oil filter -   64 Oil filter inlet channel -   66 Thermostat valve -   68 Return line -   70 Bearing -   72 Nozzle -   76 Safety valve -   78 Bypass line -   80 Relief valve -   82 Oil level sensor -   100 Spring-loaded closing mechanism -   102 Spring -   104 Closure element 

1-5. (canceled)
 6. A screw compressor for a utility vehicle, comprising: at least one housing; and one relief valve, wherein the relief valve has a spring-loaded closing mechanism with at least one spring and with at least one closure element, and the spring has a spring force configured such that said spring actuates the closure element when a predefined minimum pressure above atmospheric pressure is reached.
 7. The screw compressor as claimed in claim 6, wherein the spring is a helical spring.
 8. The screw compressor as claimed in claim 7, wherein the closure element is a ball.
 9. The screw compressor as claimed in claim 6, wherein the closure element is a ball.
 10. The screw compressor as claimed in claim 6, wherein the spring-loaded closing mechanism is arranged in a vicinity of an inlet connector of the screw compressor.
 11. The screw compressor as claimed in claim 10, wherein the spring-loaded closing mechanism is arranged in a ventilation line from the relief valve to the inlet connector of the screw compressor. 